f you've ever looked at your dirt bike tyre and wondered whether 80/100-21 is the same as 3.00-21, you're not alone.
One of the most common questions we get in the workshop is:
"Which tube fits my tyre?"
Metric and imperial tyre sizes can be confusing, especially since many older bikes use imperial (inch) sizing, while most modern motocross, enduro and trail bikes use metric sizing.
The good news? Choosing the correct motorcycle tube is much easier than it looks.
Metric vs Imperial Tyre Sizes
Motorcycle tyres are commonly labelled using either imperial (inch) sizing or metric sizing.
Although they look different, many metric and imperial tyre sizes are commonly used as equivalents.
Imperial (inch) sizing
Examples:
- 2.75-21
- 3.00-21
- 4.10-18
- 4.60-18
The first number is the tyre width in inches.
Metric sizing
Examples:
- 80/100-21
- 90/90-21
- 110/100-18
- 120/90-18
The first number is the tyre width in millimetres.
The second number is the aspect ratio, which is the sidewall height expressed as a percentage of the tyre width.
💡 Quick Tip
Motorcycle tubes are designed to fit a range of tyre sizes - not just one specific size.
For example, a 2.75/3.00-21 tube is commonly used with both 80/100-21 and 90/90-21 tyres.
Metric and Imperial Tyre Size Comparison
The table below shows the most common metric and imperial tyre size equivalents you'll find on dirt bikes.
| Metric | Imperial Equivalent |
|---|---|
| 70/100-19 | 2.50-19 |
| 80/100-21 | 3.00-21 |
| 90/90-21 | 3.00-21 |
| 90/100-21 | 3.25-21 |
| 100/90-19 | 3.50-19 |
| 100/100-18 | 4.00-18 |
| 110/90-19 | 4.50-19 |
| 110/100-18 | 4.50-18 |
| 120/80-19 | 4.60-19 |
| 120/90-18 | 4.60-18 |
Which Tube Should You Buy?
Tube manufacturers often list several compatible tyre sizes on the packaging, so don't be surprised if your tube fits more than one tyre size.
Front
| Tyre Size | Recommended Tube |
|---|---|
| 80/100-21 | 2.75/3.00-21 |
| 90/90-21 | 2.75/3.00-21 |
| 90/100-21 | 3.00/3.25-21 |
Rear
| Tyre Size | Recommended Tube |
|---|---|
| 100/100-18 | 4.00-18 |
| 110/100-18 | 4.50-18 |
| 120/90-18 | 4.50/5.10-18 |
| 120/80-19 | 4.50/5.10-19 |
If your tyre falls between two sizes, choose a tube whose recommended size range includes your tyre.
Common Dirt Bike Tube Sizes
These are the sizes we see most often in our workshop.
| Bike Type | Front Tube | Rear Tube |
|---|---|---|
| 125cc Motocross | 2.75/3.00-21 | 4.00-19 |
| 250F / 450F Motocross | 2.75/3.00-21 | 4.50-19 |
| 250/300 Enduro | 2.75/3.00-21 | 4.50-18 |
| Trail Bikes (CRF230F, TTR230, KLX230 etc.) | 2.75/3.00-21 | 4.50-18 |
| Adventure Bikes (21"/18" wheels) | 2.75/3.00-21 | 4.50/5.10-18 |
Why Choosing the Correct Tube Matters
Using the correct tube size helps:
- Reduce the chance of pinch flats during installation
- Prevent folds and wrinkles inside the tyre
- Improve reliability
- Reduce the risk of premature tube failure
A tube that's too small has to stretch more than intended.
A tube that's too large can wrinkle inside the tyre, creating wear points over time.
Quality Tubes Make a Difference
At JR Motorcycles, we stock quality motorcycle tubes from:
We stock IRC and Vee Rubber tubes in many of the most common dirt bike sizes. Whether you're replacing a punctured tube or fitting new tyres, we'll help you choose the correct tube for your bike.
Need New Dirt Bike Tyres Too?
We also stock popular off-road tyres including:
Whether you're riding motocross, trail or enduro, we can help you choose a tyre that suits your riding style and terrain.
Frequently Asked Questions
🤔❓Can I use a 3.00-21 tube in an 80/100-21 tyre?
📝Yes. A 2.75/3.00-21 tube is commonly used in both tyre sizes.
🤔❓Should I replace the tube when fitting a new tyre?
📝We generally recommend replacing the tube when fitting a new tyre, especially if the existing tube is several years old or has been repaired previously.
🤔❓Are heavy-duty tubes worth it?
📝For trail, enduro and adventure riding, heavy-duty tubes provide better puncture resistance than standard tubes. The trade-off is a small increase in weight.
🤔❓Can I reuse an old tube?
📝You can if it's in excellent condition, but we recommend inspecting it carefully for patches, cracks, stretched valve stems or signs of wear before reusing it.
Not Sure What Fits?
Not sure which tube is right for your bike?
Bring your bike into our Rolleston workshop, give us a call, or simply send us a photo of the tyre size printed on the sidewall.
We fit motorcycle tyres and tubes every day in our Rolleston workshop, so if you're unsure what fits your bike, we're happy to help. Get in touch, visit us in-store, or browse our range of IRC and Vee Rubber tubes online.
Note: Tyre size conversions are intended as a general guide. Always check your motorcycle manufacturer's recommendations and the tube manufacturer's specified size range before fitting a new tube.